Wear-resistant, superabrasive compacts are utilized in a variety of mechanical applications. For example, polycrystalline diamond compacts (“PDCs”) are used in drilling tools (e.g., cutting elements, gage trimmers, etc.), machining equipment, bearing apparatuses, wire-drawing machinery, and in other mechanical apparatuses.
PDCs have found particular utility as superabrasive cutting elements in rotary drill bits, such as roller cone drill bits and fixed cutter drill bits. A PDC cutting element typically includes a superabrasive diamond layer (also known as a diamond table). The diamond table is formed and bonded to a substrate using an ultra-high pressure, ultra-high temperature (“HPHT”) process. The PDC cutting element may also be brazed directly into a preformed pocket, socket, or other receptacle formed in a bit body. The substrate may often be brazed or otherwise joined to an attachment member, such as a cylindrical backing. A rotary drill bit typically includes a number of PDC cutting elements affixed to the bit body. It is also known that a stud carrying the PDC may be used as a PDC cutting element when mounted to a bit body of a rotary drill bit by press-fitting, brazing, or otherwise securing the stud into a receptacle formed in the bit body.
Conventional PDCs are normally fabricated by placing a cemented-carbide substrate into a container or cartridge with a volume of diamond particles positioned on a surface of the cemented-carbide substrate. A number of such cartridges may be loaded into a HPHT press. The substrates and volume of diamond particles are then processed under HPHT conditions in the presence of a catalyst material that causes the diamond particles to bond to one another to form a matrix of bonded diamond grains defining a polycrystalline diamond (“PCD”) table. The catalyst material is often a metal-solvent catalyst, such as cobalt, nickel, iron, or alloys thereof that is used for promoting intergrowth of the diamond particles.
In one conventional approach, a constituent of the cemented-carbide substrate, such as cobalt from a cobalt-cemented tungsten carbide substrate, liquefies and sweeps from a region adjacent to the volume of diamond particles into interstitial regions between the diamond particles during the HPHT process. The cobalt acts as a catalyst to promote intergrowth between the diamond particles, which results in formation of bonded diamond grains. Often, a solvent catalyst may be mixed with the diamond particles prior to subjecting the diamond particles and substrate to the HPHT process.
The solvent catalyst dissolves carbon from the diamond particles or portions of the diamond particles that graphitize due to the high temperature being used in the HPHT process. The solubility of the stable diamond phase in the solvent catalyst is lower than that of the metastable graphite under HPHT conditions. The undersaturated graphite tends to dissolve into the solvent catalyst and the supersaturated diamond tends to deposit or grow between existing diamond particles to form diamond-to-diamond bonds. Accordingly, diamond grains become mutually bonded to form a matrix of PCD with interstitial regions between the bonded diamond grains being occupied by the solvent catalyst.
The presence of the solvent catalyst in the PCD table is believed to reduce the thermal stability of the PCD table at elevated temperatures. For example, the difference in thermal expansion coefficient between the diamond grains and the solvent catalyst is believed to lead to chipping or cracking of the PCD table during drilling or cutting operations, which consequently can degrade the mechanical properties of the PCD table or cause failure. Additionally, some of the diamond grains can undergo a chemical breakdown or back-conversion to graphite via interaction with the solvent catalyst. At elevated high temperatures, portions of diamond grains may transform to carbon monoxide, carbon dioxide, graphite, or combinations thereof, thus, degrading the mechanical properties of the PDC.
One conventional approach for improving the thermal stability of PDCs is to at least partially remove the solvent catalyst from the PCD table of the PDC by acid leaching. However, removing the solvent catalyst from the PCD table can be relatively time consuming for high-volume manufacturing.
Another conventional approach is to use a carbonate material, such as magnesium carbonate, as a catalyst to promote bonding of diamond particles and form PCD. For example, U.S. Pat. Nos. 5,624,756 and 7,261,753 disclose PCD materials sintered in the presence of a carbonate material. While such PCD materials may have enhanced thermal stability, employing a carbonate material as a catalyst may present processing challenges that are not typically experienced when using a metal-solvent catalyst, such as cobalt.
Therefore, manufacturers and users of PCD continue to seek improved thermally-stable PCD materials and processing techniques.